2,2,4,4-tetramethyl-1,3-dioxolane

LiBp4, wet CH3CN. Unsubstituted 1,3-dioxolanes are cleaved slowly under these conditions (40% in 5 h). The 4,5-dimethyl- and 4,4,5,5-tetramethyl-dioxolane and 1,3-dioxane are inert under these conditions. Dimethyl ketals are readily cleaved. 

Similarly, 5-methyl-2-furaldehyde was converted into 3,4,6-tri-deoxy-DL-hex-3-enopyranosides. 4,4,5,5-Tetramethyl-2-(5-methyl-2-furyl)-l,3-dioxolane was oxidized with bromine-water, and the unsat-urated dioxolane resulting was immediately reduced with sodium borohydride, to give a mixture of DL-2-(l,4-dihydroxy-cts-pentenyl)-4,4,5,5-tetramethyl-l,3-dioxolane. Methanolysis gave the known methyl 3,4-6-trideoxy-a-DL-threo- and -en/f/iro-hex-3-enopyranosides, identified by H-n.m.r. spectroscopy.24 ... 

It was possible to obtain from 2-acetoxy-4,4,5,5-tetramethyl-l-3-dioxolan [64] a solution in which more than 90% of it had been converted into... 

Breakdown of the hemiorthoester intermediate was also found to be rate-limiting in acidic solutions with substituted 2-phenyl-2-methoxy-1,3-dioxolans [71] (substituents p-MeO, p-Me, p-F, p-Cl, p-Br, m-Cl and p-NOz) (Ahmad et al., 1979), 2-phenyl-2-methoxy-4,4,5,5-tetramethyl-l,3-dioxolan [72] (McClelland et al., 1979a), the orthoester [73] derived from exo.exo-2,... 

Diamino-2,7-bis(l,3-dioxolan-2-yl)-4,5-dimethyloctane (68) [a bis(cycloa-cetal) of the corresponding dialdehyde] gave 2,4a,6,8a-tetramethyl-3,4,4a,7,8,8a-hexahydro-l,5-naphthyridine (69) (1M H2SO4 no details).196... 

The PE spectrum of 3,3,5,5-tetramethyl-l,2-dioxolane has been studied as part of a series of cyclic peroxides. The effect of oxygen lone pair orbital dihedral angle on the ionization potential has been evaluated and the observed splitting of 1.15 eV (9.25,10.40 eV) is explained by a dihedral angle of 30 5° (75CJC3439). 

The complex formed on addition of cuprous iodide to a solution of a lithium dialkylamide in ether or tetrahydrofuran is effective in the reductive coupling of allylic halides to give 1,5-dienes with preservation of stereochemistry. This method has been used5 for the stereospecific synthesis of all-trans-squalene and (E,Z,Z,E) squalene from (E,E)- and (Z,JE)-farnesyl bromides, respectively. In an attempted synthesis of (3S)-squalene-2,3-epoxide, 4-[(4R)-2,2,5,5-tetramethyl-l,3-dioxolan-4-yl]butan-2-one (1) and the phosphonium iodide (2) were prepared.6 Unfortu-... 

Another representative example of a homolytic perester fragmentation is given by the thermal decarboxylation of y9-peroxylactones such as 4,4,5,5-tetramethyl-l,2-dioxolan-3-one [569] cf. Eq. (5-63). 

Hydrazon - Keton) 1,2-Dioxolan 5-Oxo-tetramethyl-E13/1, 849 (/J-Lacton + 02) Essigsaure... 

Dioxolan-2-enium 2-Ethyl-4,4,5,5-tetramethyl- (perchlorat) ES, 59f. (1,2-Diol +... 

CuHjjOj (Continuation) Decansaure 2-Methyl E19a, 651 (Carbonsiiure + En) E21a, 839f./846 (CO-NR2 - COOH), 1025 [C(OR) = NR - COOH] 1,3-Dioxolan 5-Butyl-2,2,4,4-tetramethyl- E14a/1, 291 (Keton -I- Oxiran)... 

The hydrolysis rates of 1,3-dioxolanes are decreased by substitution of four methyl groups at the positions 4 and 5. 2,4,4,5,5-Pentamethyl-l,3-dioxolane reacts 6.5 times more slowly than 2-methy 1-1,3-dioxolane [161]. The AS value is decreased by 9 eu. A Hammett p value of—2.0 has been found for the substituent effect on the hydrolysis of 2-phenyl-4,4,5,5-tetramethyl-l,3-dioxolane in dilute aqueous hydrochloric acid [167]. The data obey the simple Hammett equation, and it is not necessary to apply o+ values. For the reaction of the unsubstituted 2-phenyl-4,4,5,5-tetramethyl compound, the solvent isotope effect is kH/kD = 0.42, and AS is —14.2 eu. General catalysis by formic acid has been observed in the hydrolysis of the p-methoxy compound. However, the rate is not significantly increased by addition of strong nucleophiles. 

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